Purpose of the study is to assess renal function in renal transplant patients. Kidney function is determined by administering renal markers-- PAH, Iothalamate and Cephalexin to renal transplant pts to study active tubular anionic secretion, filtration, and active tubular secretion. 12 kidney transplant pts will be divided into 2 groups, 6 will receive Iothalamate and PAH over a 3 hr period, the other 6 will receive Cephalexin as a bolus and studied over 8 hrs. Drugs will be assayed in plasma and urine collected, and results compared w/6 normals receiving Ioth/PAH.